How to inspect websocket traffic with charlesproxy for iOS simulator/devices

I would like to inspect network traffic going through web sockets, I have no control over the networking code as this is a binary lib for which I do not have the source code, so I cannot do any log/breakpoint in the networking part of the code.

I have tried using the latest version of CharlesProxy which claim to be able to sniff websockets however when I tried the url and apis using websockets were not even mentionned in the list of endpoints called from my iPhone.

I have verified that CharlesProxy is configured correctly as I am able to inspect non-websocket traffic even under SSL.

So my question is: did anyone find a solution to inspect traffic going through websockets with CharlesProxy?